Recently, in a manufacturing process of a semiconductor device, a design rule is getting miniaturized. Along with such a trend, an organic film having a low dielectric constant, i.e., a low-k film is used as an interlayer insulating film and Cu having a lower electric resistance than a traditionally used Al is utilized in a wiring layer in order to achieve a high speed operation.
When Cu wiring multi-layers are formed while interposing interlayer insulating films therebetween, a low-k film made of, e.g., polymer is formed as an interlayer insulating film on, e.g., a semiconductor wafer (hereinafter, simply referred to as a ‘wafer’) provided with a certain layer, and via etching is performed by using a resist layer or the like as a mask. Thereafter, the resist and the polymer are removed, and then a sacrificial layer is formed, and trench etching is performed by using a resist layer as a mask. Then, the resist and the polymer are removed again, and dry asking and cleaning are performed. Then, the sacrificial film and a stopper layer are removed by etching, and a Cu wiring layer and a plug are formed.
Thereafter, the Cu wiring layer is polished by CMP (Chemical Mechanical Polishing). Subsequently, a Cu oxide film on a surface thereof is removed by a plasma process or a wet process. Then, a low-k film is additionally formed thereon as an interlayer insulating film.
In such a case, since Cu tends to be diffused readily, Cu may be diffused into the low-k film due to a temperature rise in the process of forming the low-k film. This has an adverse influence on a device. In this regard, there has been proposed a technology for preventing a diffusion of Cu by forming any one of SiN, SiO2, SiC, SiCO and SiCN on the entire surface of the wafer as a Cu diffusion barrier film by plasma CVD after performing CMP (see, for example, T. Saito et al. in proceeding of IITC, 2001, pp. 15 to 17).
However, since these materials have high dielectric constants (for example, SiN has a relative dielectric constant of about 7), the effect thereof decreases even if a low-k film having a relative dielectric constant of about 2 to 3 is used as an interlayer insulating film.